1. Field of the Invention
The present invention relates to an active matrix light-emitting device, and more particularly, a structure of a portion for extracting light.
2. Related Art
A light-emitting device utilizing light from an electroluminescent element (light-emitting element) has attracted attention as a low power consumption display device having a wide viewing angle.
As a driving method for a light-emitting device that is used mainly as a display device, an active matrix driving method and a passive matrix driving method can be used. An active matrix light-emitting device can control emission and non-emission of every light-emitting element. Therefore, an active matrix light-emitting device can operate with lower power consumption than that of a passive matrix light-emitting device. The active matrix light-emitting device is suitable for mounting to not only a display portion of a small electric appliance such as a cellular phone but also a display portion of a large TV set.
In an active matrix light-emitting device, a circuit for controlling the drive of each light-emitting element is provided to each of the light-emitting element. The circuit and the light-emitting element are provided over a substrate so that extraction of light to the exterior is not prevented by the circuit. A portion overlapped with the light-emitting element is provided with a laminated insulating layer having a light transmitting property. Light is emitted outside by passing through the insulating layer. The insulating layer is provided to form a circuit element such as a transistor or a capacitor element, each of which is a component of the circuit; or a wiring.
When light passes through the laminated insulating layer, light emission may multiply interacted with each other due to the difference of refractive index of each the insulating layer. As a result, an emission spectrum is varied depending on an angle of viewing a light extraction surface, which leads to a problem of deterioration of visibility of an image displayed on the light-emitting device.
The deterioration of visibility of an image due to the difference of refractive index of each layer may be occurred in a passive matrix light-emitting device. For example, Unexamined Patent Publication No. 7-211458 disclosed a light-emitting element with an improved structure to solve a problem of deterioration of visibility of an image caused by the reflection of external light and light emission at an interface due to the difference of refractive index of each layer composing a light-emitting element.